4,084 research outputs found
The origin of emission and absorption features in Ton S180 Chandra observations
We present new interpretation of Ton S180 spectrum obtained by {\it Chandra}
Spectrometer (Low Energy Transmission Grating). Several narrow absorption lines
and a few emission disk lines have been successfully fitted to the data. We
have not found any significant edges accompanying line emission. We propose the
interpretation of narrow lines consistent with the paper recently written by
Krolik (2002), where warm absorber is strongly inhomogeneous. Such situation is
possible in so called multi-phase medium, where regions with different
ionization states, densities and temperatures may coexist in thermal
equilibrium under constant pressure. We illustrate this scenario with
theoretical spectra of radiation transfered through a stratified cloud with
constant pressure (instead of constant density) computed by code {\sc titan} in
plane parallel approximation. Detected spectral features are faint and their
presence do not alter the broad band continuum. We model the broad band
continuum of Ton S180 assuming an irradiated accretion disk with a dissipative
warm skin. The set of parameters appropriate for the data cannot be determined
uniquely but models with low values of the black hole mass have too hot and
radially extended warm skin to explain the formation of soft X-ray disk lines
seen in the data.Comment: accepted to Ap
Recurrence Relations for Strongly q-Log-Convex Polynomials
We consider a class of strongly q-log-convex polynomials based on a
triangular recurrence relation with linear coefficients, and we show that the
Bell polynomials, the Bessel polynomials, the Ramanujan polynomials and the
Dowling polynomials are strongly q-log-convex. We also prove that the Bessel
transformation preserves log-convexity.Comment: 15 page
The puzzle of the soft X-ray excess in AGN: absorption or reflection?
The 2-10 keV continuum of AGN is generally well represented by a single power
law. However, at smaller energies the continuum displays an excess with respect
to the extrapolation of this power law, called the ''soft X-ray excess''. Until
now this soft X-ray excess was attributed, either to reflection of the hard
X-ray source by the accretion disk, or to the presence of an additional
comptonizing medium, giving a steep spectrum. An alternative solution proposed
by Gierlinski and Done (2004) is that a single power law well represents both
the soft and the hard X-ray emission and the impression of the soft X-ray
excess is due to absorption of a primary power law by a relativistic wind. We
examine the advantages and drawbacks of reflection versus absorption models,
and we conclude that the observed spectra can be well modeled, either by
absorption (for a strong excess), or by reflection (for a weak excess). However
the physical conditions required by the absorption models do not seem very
realistic: we would prefer an ''hybrid model''.Comment: 4 pages, 3 figures, abstracts SF2A-2005, published by EDP-Sciences
Conference Serie
Human thyroid tumours, the puzzling lessons from E7 and RET/PTC3 transgenic mice
Human rearranged RET/PTC3 (papillary thyroid carcinoma) proto-oncogene and high-risk human papillomavirus (HPV) type 16 E7 oncogene induces in the mouse a neoplastic transformation of thyroid follicular cells. We present a detailed immuno-histological study (170 mouse thyroids: RET/PTC3, E7, wild type, 2- to 10-month-old) with cell cycle proliferation and signalling pathway indicators. The characteristics of both models are different. There is an âoncogene dependent' cellular signature, maintained at all studied ages in the E7 model, less in the RET/PTC3 model. During tumour development a large heterogeneity occurred in the Tg-RET/PTC3 model within a same tumour or within a same thyroid lobe. The Tg-E7 model was less heterogeneous, with a dominant goitrous pattern. The solid tumour already described in the RET/PTC3 models associated with cribriform patterns, suggested âPTC spindle cell changes' as in humans PTC rather than the equivalent of the solid human PTC. Proliferation and apoptosis in the two thyroid models are related to the causal oncogene rather than reflect a general tumorigenic process. The thyroids of RET/PTC3 mice appeared as a partial and transient model of human PTCs, whereas the Tg-E7 mice do not belong to the usual PTC type
Snow spectral albedo at Summit, Greenland: measurements and numerical simulations based on physical and chemical properties of the snowpack
The broadband albedo of surface snow is determined both by the near-surface profile of the physical and chemical properties of the snowpack and by the spectral and angular characteristics of the incident solar radiation. Simultaneous measurements of the physical and chemical properties of snow were carried out at Summit Camp, Greenland (72°36ÂŽ N, 38°25ÂŽ W, 3210 m a.s.l.) in May and June 2011, along with spectral albedo measurements. One of the main objectives of the field campaign was to test our ability to predict snow spectral albedo by comparing the measured albedo to the albedo calculated with a radiative transfer model, using measured snow physical and chemical properties. To achieve this goal, we made daily measurements of the snow spectral albedo in the range 350â2200 nm and recorded snow stratigraphic information down to roughly 80 cm. The snow specific surface area (SSA) was measured using the DUFISSS instrument (DUal Frequency Integrating Sphere for Snow SSA measurement, Gallet et al., 2009). Samples were also collected for chemical analyses including black carbon (BC) and dust, to evaluate the impact of light absorbing particulate matter in snow. This is one of the most comprehensive albedo-related data sets combining chemical analysis, snow physical properties and spectral albedo measurements obtained in a polar environment. The surface albedo was calculated from density, SSA, BC and dust profiles using the DISORT model (DIScrete Ordinate Radiative Transfer, Stamnes et al., 1988) and compared to the measured values. Results indicate that the energy absorbed by the snowpack through the whole spectrum considered can be inferred within 1.10%. This accuracy is only slightly better than that which can be obtained considering pure snow, meaning that the impact of impurities on the snow albedo is small at Summit. In the near infrared, minor deviations in albedo up to 0.014 can be due to the accuracy of radiation and SSA measurements and to the surface roughness, whereas deviations up to 0.05 can be explained by the spatial heterogeneity of the snowpack at small scales, the assumption of spherical snow grains made for DISORT simulations and the vertical resolution of measurements of surface layer physical properties. At 1430 and around 1800 nm the discrepancies are larger and independent of the snow properties; we propose that they are due to errors in the ice refractive index at these wavelengths. This work contributes to the development of physically based albedo schemes in detailed snowpack models, and to the improvement of retrieval algorithms for estimating snow properties from remote sensing data
Conséquences de l'hypertrophie musculaire héréditaire sur la trame conjonctive du muscle de bovin
International audienc
CONSĂQUENCES DE L'HYPERTROPHIE MUSCULAIRE HĂRĂDITAIRE SUR LA TRAME CONJONCTIVE DU MUSCLE DE BOVIN
Conséquences de l'hypertrophie musculaire héréditaire des bovins sur la musculature. II. - Importance relative des différentes régions
International audienc
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